Porous membranes are used in a wide variety of engineering applications. Such membranes are often used in gas or vapor separation, reverse osmosis, electrochemical applications, hyperfiltration, ultrafiltration and microfiltration. Such membranes can even be used for the manipulation of chemical reactions including selective ion separation. The membranes are usually thin, two dimensional bodies which are normally less than 0.5 mm thick and contain upwards of 20% porosity. The pores in these membranes have radii ranging in size from a few nanometers to several microns. The flux of liquids or gas through the membrane is in most cases driven by a gradient of pressure or an electric field.
Traditional methods of making such porous membranes have involved the deposition of adherent and highly continuous layers of materials such as alumina and aluminum. These materials are known to have been deposited using a number of techniques, such as tape casting, extrusion, vapor deposition. both physical vapor deposition (PVD) and chemical vapor deposition (CVD), and by electrochemical methods. Tape casting and extrusion are limited in the range of materials that can be used to make porous membranes. The degree of membrane porosity or pore density obtainable with either of these techniques is also limited. Vapor deposition is an extremely slow and costly process and does not lend itself to making large parts. Other techniques such as electrochemical methods are also known to suffer from such size limitations. In addition, the type of materials that may be applied by some electrochemical methods are severely limited. Sol-gel and hydrothermal techniques for making porous membranes are also known. The limitations of these techniques have been documented in a book on the subject by Ramesh Bhave (Inorganic Membranes, van Nostrand 1991). For instance, these techniques may be cost prohibitive and compatible with only a limited number of materials. In addition, the use of sol-gel techniques to form porous membranes has been discussed in an article by Y. S. Lin and A. J. Burggraaf, J.Amer. Ceram. Soc., Vol. 4, 1991, page 219.
Several known materials have properties such as high temperature and corrosion resistance, which would be useful in some porous membrane applications. While some of these materials have been used with prior methods, like those mentioned above, to make such porous membranes, a number of these materials have not, for various reasons, including incompatibility with those prior methods. Those prior materials and methods which have proven compatible and which can produce useful membranes are typically involved and costly.
Therefore, there is a need for a more cost effective method of making porous membranes not only with materials known for such use but also with materials having desirable properties but which previously have not been known for making such membranes.